In a known seal chain, described in Japanese Laid-Open Patent Publication No. 2004-256262, a rigid sealing ring is in contact with an axial end surface of the bushing, and an elastic sealing ring is compressed between the rigid ring and an outer link plate.
In another known seal chain, described in Japanese Laid-Open Patent Publication No. 2005-282813, lubricating oil is sealed between a bushing and a roller by seals comprising concave portions formed on an inside surfaces of the inner link plates and surrounding the ends of the roller. Ring-shaped seal plates are loosely fitted on both end portions of said roller, and an elastic ring is disposed between each concave portion and the adjacent seal plate.
In the seal chain of Japanese Patent Publication No. 2004-256262, compression of the elastic ring between the bushing and the outer link plate imposed resistance to bending of the chain. The resistance to bending of the chain can be reduced by surface finishing of the inside surfaces of the outer link plates and the end surfaces of the bushings that contact the rigid rings. However, surface finishing requires additional manufacturing steps that increase the cost of manufacture of the chain. In addition, since rigid rings are provided in addition to the elastic sealing rings, the number of chain parts is increased and assembly of the chain becomes more difficult and costly.
On the other hand, in the seal chain of Japanese Patent Publication No. 2005-282813, since a sealing ring and a seal plate are in a compressed state between a concave portion on an inside surface of an inner link plate and the roller, resistance to relative rotation of the roller and the inner link plate is increased, preventing the roller from rotating smoothly during operation of the chain. Here again, the problem of resistance to relative rotation can be addressed by surface finishing of the seal plates, the inside surfaces of the inner link plates, and the end surfaces of the rollers, but the surface finishing steps increase the cost and difficulty of manufacture. Moreover the provision of the seal plate and the sealing ring increases the number of parts, also making assembly difficult and increasing manufacturing cost.
Accordingly, the invention has one or more of the following objects. A first object of the invention is to solve the above-mentioned problems. Another object is to provide an oil-free chain which prevents leakage of lubricating oil sealed between a connecting pin and a bushing and between a roller and the bushing. Still another object is to prevent invasion of dust during operation of the chain, without reducing strength of the chain. Other objects of the invention include the reduction of sliding contact wear between an outer circumferential surface of the connecting pin and an inner circumferential surface of the bushing, suppression of sliding sounds, and avoidance of seizing of the outer circumferential surfaces of the bushings and the inner circumferential surfaces of the rollers. Finally, it is an object of the invention to provide a seal chain in which the number of parts is small, and which can be assembled and disassembled easily and at low cost.